1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2007-33770, Japanese Patent Application Laid-open No. 2006-195281, and Japanese Patent No. 3041808 disclose image forming apparatuses that adjust image forming conditions when a predetermined condition is satisfied, for example, immediately after the power of the image forming apparatus is turned on, or when the accumulated number of sheets fed for print output reaches a predetermined number. In an operation for adjusting the image forming condition, for example, light is emitted from a light emitting unit, such as a light emitting diode (LED), of an optical sensor and then reflected by the surface of a photosensitive element that functions as a latent image carrier or a transfer belt that functions as an image carrier. The amount of reflected light is then detected by a light receiving element of the optical sensor. After a reference toner image with a predetermined shape is formed on the surface of the photosensitive element, the amount of light reflected by the reference toner image formed on the surface of the photosensitive element or the transfer belt to which the reference toner image is transferred from the photosensitive element is detected by the optical sensor. The amount of toner adhering to the reference toner image per unit area is determined on the basis of the ratio between the amounts of reflected light and thus the image forming conditions for image forming processes are adjusted accordingly. The image forming conditions include the electric potential of a uniformly charged photosensitive element, developing bias, optical writing intensity for a photosensitive element, or a control target value of the toner density of a developer. The image density is controlled by adjusting the image forming conditions so that it is possible to print images with a stable image density over a long time.
Japanese Patent No. 3741691 and Japanese Patent Application Laid-open No. 2007-114429 disclose image forming apparatuses that include a toner sub-container called a sub-hopper that is arranged along a toner conveying path for conveying toner from a toner cartridge to a developing unit. The toner cartridge contains toner to be supplied to the developing unit. Such an image forming apparatus performs an operation for supplying toner to the developing unit by a toner filling operation to temporarily fill a sub-hopper with toner fed from the toner cartridge and a toner supply operation to supply the toner contained in the sub-hopper to the developing unit depending on the requirements of the developing unit.
If a problem occurs in an image forming process during the operation for adjusting the image forming condition, the reference toner image is not correctly formed. The incorrectly formed reference toner image is detected by an optical reflection sensor. For example, if charging bias is turned off while developing bias is correctly turned on, solid images are formed on a whole surface with no image density adjustment; therefore, the optical reflection sensor detects abnormally dark images. If a mechanism for supplying toner from the toner cartridge to the developing unit cannot be operated, the toner is not supplied from the toner cartridge to the developing unit even though the toner contained in the developing unit has been consumed; therefore, the optical reflection sensor detects abnormally light images.
Although various phenomena can occur depending on a component that performs the image forming process or adjustment of image forming conditions, it is possible to determine, to some extent, that a problem has occurred in the image forming process by detecting a problem with the reference toner image. However, because it is difficult to determine the cause of the problem in the image forming process only by detecting a problem with the reference toner image, in a conventional image forming apparatus, maintenance personnel need to separately analyze whether each component that performs the image forming process is operating correctly or incorrectly after the problem is detected, whereby the problem can be resolved.
When a problem is detected in an image forming process performed by an image forming apparatus that includes a sub-hopper, a process for resolving the problem is performed as described below.
If a control unit determines that a problem has occurred in an image forming process on the basis of a detection result of a reference toner image, a notifying unit, such as an operation panel, notifies the user of the occurrence of the problem in the image forming process. The user then calls maintenance personnel, and the maintenance personnel analyze the cause of the problem and repair the part of the image forming apparatus that is causing the problem. In a conventional image forming process, maintenance personnel need to examine whether a problem has occurred in every part of the image forming apparatus that can affect the reference toner image. Therefore, even though a problem may have occurred in a toner-filling operation to fill a sub-hopper with toner, the maintenance personnel need to separately analyze whether each component of an image forming unit, such as a developing unit, arranged around a photosensitive element is operating correctly or incorrectly. Therefore, it takes a long time for the maintenance personnel to determine that the problem has occurred in the toner filling process, resulting in a long downtime during which the maintenance personnel repair the image forming apparatus and the user cannot use the image forming apparatus.